Volume XXII |

Flood risk modelling using HEC-RAS and GIS in the semi-urban water-shed of Oued Ziad (Constantine, North-Eastern Algeria)

Abstract: The study of flood risk in Algerian cities has become essential given the multiple issues at stake (urbanization, urban sprawl, easements, infrastructure, soil structure, etc.), which constitute vulnerable elements, as well as their frequen-cy and repetition in time and space. This has become a problem for the city and the urban environment, particularly in large metropolises such as Constantine. The watershed of Oued Ziad located in the northwestern part of the city of Constantine has experienced exceptional flooding, causing loss of life and property in the Jebli Ahmed agglomeration in the Hamma Bouziane township. The main objective of this research is to identify the factors aggravating the risk of flooding in the Oued Ziad watershed, to analyze the frequency of maximum daily rainfall to determine peak flows for different return periods of 10, 20, 50, 100 and 1000 years, and to map the extent of the flood hazard in the Oued Ziad watershed for a centennial flow, using geographic information systems and HecRas software. The simulation results show the overflow of Oued Ziad on national road N°27, affecting a part of the agglomeration located downstream by a centennial peak flow equal to 50. 98 m3/s and a water height exceeding 3 m, which confirms the extent of the area exposed to risk during the flood that occurred on 19/9/2018. The field survey shows that several anthropic factors in-crease the risk of flooding while the capacity of the existing hydraulic structures is insufficient to evacuate water during floods, which requires the development of this watercourse and its banks to protect the population and its property from the risk of flooding and to reduce the impact on the city’s environment and socio-economic activities.

Volume XX |

Risk of Dynamics of the River Stream in Tectonic Areas. Case studies: Curvature Carpathian – Romania and Maghrebian Chain – Algeria

Abstract: The tectonic characteristics of the Alpine orogeny highlight some similarities in the genesis of landforms over large areas. This paper analyses the role of tectonic processes in two subsiding areas with uplift movements. The overall tectonic activity implies the formation and evolution of the hydrographic network and its correlation with the major relief structure, thus forming streams parallel to the high-altitude lines, as well as consistent, transversal, and subsequent streams.These tectonic processes are accompanied by antecedents and/or epigenesis common in the Eastern Carpathians, Romania. Hence the Bistrița River is longitudinal compared to the Bistrița and the Stânișoara Mountains, but also transversal in other sectors. In Algeria, the Northeast, especially the Zighoud Youcef zone (NE of Constantine), is characterized by a particular morphography and morphometry of the river basins which reveals reorganizations of the river network through their transversal or longitudinal characteristics compared to the structure and tectonics of the region. In areas with imminent catchments, the regressive erosion amplifies the slope dynamics and slope processes vulnerability.The uplift and subsidence movements impose reorganizations of the hydrographic network of the catchments with the alternation of the erosion and sedimentation processes it creates a certain fluvial style pattern. In the subsidence of the Întorsura Buzăului depression, the longitudinal profile of the Buzău River has a very low slope and its meanders create islets. This is subject to frequent floods which imposed the riverbed regularization. However, in Zighoud Youcef, the Oued Smendou River also indicates some similarities with the Buzău River structure due to subsiding areas of the Mila-Constantine basin.